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Parallel operation of grid-forming inverters (GFMIs) is often achieved using droop characteristics implemented in converter controllers. Converters' recovery after a disturbance depends on the dynamics of each individual GFMI, and the droop characteristic alone is unable to ensure successful parallel operation. This work proposes a dynamic-phasor based modeling approach that enables eigenvalue analysis of multi-converter systems to identify the underlying factors that affect the interactions among parallel GFMIs. Network dynamics are included through dynamic phasor modeling of its elements, and controller dynamics are fully included. Modeling modularity is preserved, which allows to easily extend the test system to any topology of interest. The results presented for an exemplar two-converter system prove that the virtual inertia time-constant plays a significant role in exciting interactions, and that network and control system parameters are vital in extending the stability margins of the systems. EMT simulation results from PSCAD/EMTDC are included to verify the validity of the predictions of the dynamic-phasor based model. • A modeling platform based upon dynamic phasors is developed form small-signal modeling of multi-converter systems. • Using the developed platform interactions among grid-forming converters in low-inertia systems is studied. • Several factors contributing to interactions among grid-forming converters are identified. [ABSTRACT FROM AUTHOR]

The paper presents a hybrid co-simulator comprising EMT and dynamic phasor-based simulators. The EMT simulator models portion(s) of the network wherein fast transients are prevalent and detailed modeling is necessary. The dynamic phasor solver models the rest of the network using extended-frequency Fourier components. Specialized algorithms are developed and presented to accurately map instantaneous EMT and counterpart dynamic phasor samples. Interfacing requirements for co-simulation using different time-steps in the two solvers are also discussed along with implications on accuracy and numerical stability. The paper demonstrates the developed co-simulation algorithm using an example of the IEEE three-phase 118-bus network in which a wind farm is included. The wind farm and the network in its vicinity are modeled in the PSCAD/EMTDC electromagnetic transient simulator, and are interfaced to the rest of the system modeled in a dynamic phasor-based solver. The paper demonstrates the accuracy of the proposed co-simulation for a range of time-step ratios of the two solvers, and also reports the substantial computational time savings obtained using the hybrid simulator. [ABSTRACT FROM AUTHOR]

This paper introduces new techniques for efficient use of electromagnetic transient simulators combined with optimization algorithms to optimize power systems with converter-tied renewable resources. This work is motivated by several challenges that must be overcome for simulation-based optimal design, including high computational burden of simulating large switching systems, repetitive nature of the design cycle, and large number of variables that need to be handled. Two screening methods are proposed in this paper to identify the parameters that do not influence the optimal solution significantly and hence can be ignored. Moreover, hybridization of optimization algorithms and parallel processing techniques are explored to achieve additional computational benefits. Case studies of systems with different complexity and number of variables are used to demonstrate the effectiveness of the proposed techniques. • Several new methods for accelerated simulation-based optimization of power systems are introduced. • Screening methods for removing non-influential parameters from optimization are introduced. • Parallel processing and hybrid, multi-solver algorithms are introduced. • Examples of power systems with renewable resources are shown to quantify the benefits of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents an average-value model of a line-commutated converter-based HVDC system using dynamic phasors. The model represents the low-frequency dynamics of the converter and its ac and dc systems, and has lower computational requirements than a conventional electromagnetic-transient (EMT) switching model. The developed dynamic-phasor model is verified against an EMT model of the CIGRE HVDC Benchmark. Simulation results confirm the validity and accuracy of the average value model in predicting the low-frequency dynamics of the ac- and dc-side quantities. Merits and applicability limitations of the average model are highlighted. [ABSTRACT FROM AUTHOR]

This paper extends the concept of dynamic average-value modeling to power-electronic-intensive hybrid-electric vehicular power trains. Hybrid vehicles with plug-in capability are becoming increasingly important in the study of emerging smart power grids, and their simulation using digital programs has gained widespread attention. This paper demonstrates the usefulness of averaging in preserving the dynamic characteristics of the vehicular system while reducing the computational intensity of its simulation on an Electromagnetic Transients Program-type simulator. This paper presents an example of averaging for modeling, simulation, and system-level studies of a power-split gear hybrid drive-train. [ABSTRACT FROM PUBLISHER]

This paper describes methods and issues related to interfacing electromagnetic transient simulation programs with general mathematical algorithms, which are either custom-developed by the user or are available through other mathematical analysis platforms. Various interfacing types and techniques are described along with potential areas of application. Implementation methods are detailed for each type of interface as well. This paper presents several interfacing examples from a wide variety of applications, including advanced switching schemes for power converters and controller implementation. [ABSTRACT FROM AUTHOR]

This paper presents an approach to the design of ro- bust power-electronic systems (i.e., those which have optimal operation over a range of operating configurations). Designing non- linear systems, such as power-electronic converters, to be robust is a challenging task as settings that may be optimal for a given operating configuration may be inadequate for another. This paper extends the method of combining nonlinear optimization with electromagnetic transient simulation, which has previously been successfully applied to the design of optimal systems at only one operating point; to an approach which simultaneously considers a range of operating points. The method is exemplified using two examples. In the first example, a dc power supply is designed to operate optimally over a range of current order settings. The second is the case of an HVdc system, which is optimized to work well with a range of possible ac system configurations. [ABSTRACT FROM AUTHOR]

Electromagnetic transient simulation programs (emtp-type programs) are powerful tools for the study of a wide range of power system transient problems. This paper introduces a novel tool in which an emtp-type program becomes the objective function evaluator for a nonlinear optimization algorithm. In this approach, the nonlinear optimization program is given control to perform several consecutive runs with a view to minimize (or maximize) the desired objective function, which is computed from the results of each simulation run. Since the optimization algorithm strategically selects the parameters for the emtp run, the overall design process is orders of magnitude faster than that possible from sequential or random (Monte Carlo-type) multiple-runs of the emtp-type program. The paper discusses the mechanics of the interface as well as design of objective functions. The power of the proposed method is demonstrated through two examples for the design of power-electronic converters. [ABSTRACT FROM AUTHOR]

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation. [ABSTRACT FROM PUBLISHER]

This paper deals with the current state-of-the-art in interfacing issues related to real-time digital simulators employed in the simulation of power systems and power-electronic systems. This paper provides an overview of technical challenges encountered and their solutions as the real-time digital simulators evolved. Hardware-in-the-loop interfacing for controller hardware and power apparatus hardware are also presented. [ABSTRACT FROM AUTHOR]